Bourbaki

Corollary 1

Tag 04Z6, permanent. Cite it as [Bourbaki, Tag 04Z6].

Commutative Algebra, chapter VII, § 1. Krull domains

Let A\mathbf{A} be a Krull domain, K\mathbf{K} its field of fractions and a,b\mathbf{a}, \mathbf{b} and cc three divisorial fractional ideals of A\mathbf{A} such that a⊂b\mathbf{a} \subset \mathbf{b}. There exists x∈Kx \in \mathbf{K} such that a=b∩xc\mathbf{a} = \mathbf{b} \cap x\mathbf{c}.

Let (vt)t∈I(v_t)_{t \in I} be the family of essential valuations of A\mathbf{A} and let (mt)(m_t) (resp. (nt),(pt)(n_t), (p_t)) be the family of rational integers (zero except for a finite number of indices) such that a\mathbf{a} (resp. b,c\mathbf{b}, c) is the set of x∈Kx \in \mathbf{K} for which vt(x)≥mtv_t(x) \geq m_t (resp. nt,ptn_t, p_t) for all t∈It \in I (Proposition 5, no. 4). The set J\mathbf{J} of t∈It \in I such that mt>ntm_t > n_t is finite. As pt=mt=0p_t = m_t = 0 except for a finite number of indices, Proposition 9 shows that there exists x∈K∗x \in \mathbf{K}^* such that vt(x−1)+mt=ptv_t(x^{-1}) + m_t = p_t for t∈Jt \in \mathbf{J} and

vt(x−1)+mt≥pt v_t(x^{-1}) + m_t \geq p_t
for t∈I−Jt \in I - \mathbf{J}. Then, for all t∈It \in I, mt=sup⁡(nt,vt(x)+pt)m_t = \sup(n_t, v_t(x) + p_t). Whence a=b∩xc\mathbf{a} = \mathbf{b} \cap x\mathbf{c}.

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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Transcribed from the printed volume. Not translated.